1. Field of the Invention
The present invention relates to an outer-diameter blade, an inner-diameter blade and cutting machines which respectively use the outer-diameter blade and the inner-diameter blade for cutting hard material, such as metal, ceramics, semiconductor single crystal, grass, quartz crystal, stone, asphalt or concrete, and a core drill and a core-drill processing machine which drives the core drill for forming a hole in the hard material.
2. Description of the Related Art
A conventional outer-diameter blade and a cutting machine using the conventional outer-diameter blade will be described with reference to FIGS. 18 to 21.
A conventional outer-diameter blade 10, as shown in FIG. 18, is constructed of: a metal base plate 12 having a disk-like shape, which is rotating at a high speed; and a tip portion 14 formed along the outer peripheral part thereof, in which portion diamond abrasive grains or CBN abrasive grains are fixed to the outer peripheral part by metal bonding, resin bonding or electroplating. A numerical mark 16 indicates a shaft hole which is formed in the central part of the metal base plate 12. A numerical mark 18 indicates a cutting machine and is provided with a rotation drive section 20 which includes drive means such as a motor and a rotary shaft 22 connected to the rotation drive section 20 (FIGS. 19(a) and 19(b)).
When a to-be-cut object or a workpiece G in a shape, such as a plate, a rod or a tube made of hard material, such as glass, ceramics, semiconductor single crystal, quartz crystal, stone, asphalt or concrete, is cut using a conventional outer-diameter blade, there has arisen a problem, because the cutting progresses in the following way: A shape of the tip portion 14 of the outer-diameter blade 10 is channel-like or of a Greek letter .PI. in section one end of which has an opening facing the metal base plate 12 and the other end of which is flat (FIG. 18(c)) and therefore, as cutting of the to-be-cut object G by the outer-diameter blade 10 progresses, cutting resistance arises between the to-be-cut object G and the outer-diameter blade 10 (FIG. 20(a)).
Since the cutting resistance simultaneously acts in two ways: in one way the workpiece G is warped, and in the other way the metal base plate 12 of the outer-diameter blade 10 is bowed, the to-be-cut object G is put into contact with a side surface 12a of the metal base plate 12 and as a result, chipping (a phenomenon that cracking or flaking occur on a cutting surface of the to-be-cut object G) occurs (FIG. 20(b)).
Besides, a cutting surface M is curved due to bowing (FIG. 21(b)) of the metal base plate 12 of the outer-diameter blade 10 taking place during cutting operation and eventually when the cutting is completed, the tip portion of the outer-diameter blade turns aside (FIG. 21(c)) and a burr N remains at a cut-off end of the to-be-cut object G (FIG. 21(d)).
Then, a conventional inner-diameter blade and a cutting machine using the inner-cutting blade will be described with reference to FIGS. 26 to 28.
A conventional inner-diameter blade 110, as shown in FIGS. 26 to 28, is constructed of: a base plate 114 (for example a thin metal base plate having a doughnut like shape) with a central hole 112 formed in a central part which rotates at a high speed; and a tip portion 116 formed along an inner peripheral part thereof, abrasive grains (cutting grains) of which portion are fixed to the inner peripheral part by metal bonding, resin bonding or electroplating.
In FIG. 27, a numerical mark 120 indicates a conventional cutting machine and the machine 120 is equipped with a rotary shaft 126 which is mounted to the base table 122 in a rotatable manner with a bearing member 124 interposed therebetween. A rotary cylinder 130 is mounted on the top of the rotary shaft 126. The rotary cylinder 130 is constructed of a circular bottom plate 130a and a cylindrical side plate 130b vertically set on the bottom plate 130a.
A grinding liquid waste route 128 is formed lengthwise as a hole through the central part of the rotary shaft 126 and further through the central part of the bottom plate 130a of the rotary cylinder 130 and the grinding liquid which is made to flow and falls down on the bottom plate 130a during the cutting is discharged through the waste route. An inner-diameter blade 110 of a structure shown in FIGS. 26(a) and 26(b) is mounted on the upper end of the outer peripheral portion of the cylindrical side plate 130b with a mounting plate 132 interposed therebetween.
A numerical mark 134 indicates a motor and a motor pulley 138 is attached to a motor shaft 136. A pulley 140 is mounted in a lengthwise middle part of the rotary shaft 126 in a corresponding manner to the motor pulley 138. A numeral mark 142 indicates a drive belt and the belt is extended between the motor pulley 138 and the pulley 140. When the motor is driven, the motor shaft 136 is rotated, the rotation is transmitted to the rotary shaft 126 through the motor pulley 138, the drive belt 142 and the pulley 140, and the rotary shaft 126 is eventually rotated.
The rotary cylinder 130, the mounting plate 132 and the inner-diameter blade 110 are rotated in company with rotation of the rotary shaft 126. By putting the to-be-cut object G into contact with the tip portion in rotation, the workpiece G is cut by the tip portion 116. Numerical marks 144 and 146 indicate bearings attached to outer side wall part of the rotary shaft 126.
When a to-be-cut object G in a shape, such as a plate, a rod or a tube made of hard material, such as glass, ceramics, semiconductor single crystal, quartz crystal, stone, asphalt or concrete, is cut using a conventional inner-diameter blade while the to-be-cut object G is held by a work holder H, there has arisen a problem, because the cutting progresses in the following way: A cutting resistance arises between the workpiece G and the inner-diameter blade 110 as the cutting progresses. Since the cutting resistance acts so as to bow the inner-diameter blade 110, the to-be-cut object G is put into contact with a side surface of the inner-diameter blade 110, which further causes a mechanical contact resistance.
The cutting resistance and the contact resistance cooperate with each other to an adverse effect, so that the inner-diameter blade 110 is bowed more as shown in FIG. 28(c) and as a result, a cutting surface of the to-be-cut object G is curved as observed after the cutting is finished. The inner-diameter blade 110 which has once been bowed in such a way does not restore its original shape and a to-be-cut object G which comes next is always finished in the cutting so as to have a curved cutting surface of the to-be-cut object G due to the existing deformation of the blade.
In a conventional core drill 212, as shown in FIG. 29, which is a tool, a base metal section 216 having a cup-like shape constructed of a disk-like top wall 216a and a cylindrical side wall 216b is provided on a fore-end of a shank 214 made of steel, which acts as a rotary shaft; a grinding stone portion 218 is mounted on an outer end part of the base metal section 216, whose abrasive grains are fixed to the outer end part of the base metal section 216 by metal bonding, resin bonding or electroplating; and not only are the shank 214, the base metal section 216 and the grinding stone portion 218 rotated by drive means such as a motor, but the grinding stone portion 218 is put into contact with a workpiece W so that the workpiece W can be ground through to form a circle hole in section leaving a cylindrical core therein.
A through-hole 222 along an axis of the shank 214 of the core drill 212 is formed therein in order to supply a grinding liquid 220 to a working area in grinding. For example, when a workpiece W of glass or the like is ground, the grinding liquid 220, which is fed through the through-hole 222, passes through gaps between the surfaces of the outer end face and side surfaces of the grinding stone portion 218, and the workpiece W, during which passage the grinding liquid 220 not only cools the grinding region but washes away grinding powder of the workpiece W produced by grinding and abrasive grains loosed off from the grinding stone portion 218 (hereinafter also simply referred to as workpiece powder and the like) and the grinding liquid 220 is discharged together with the workpiece power. By such an action of the grinding liquid 220, not only is a drilling speed of the core drill 212 increased but a lifetime of the grinding stone portion 218 is extended.
However, when a hole forming is performed in a workpiece W made of glass and the like with a comparatively large thickness using the conventional core drill 212, there has arisen a problem since adverse effects as follows occur: As grinding progresses and a hole depth increases, the grinding liquid 220 receives very large resistance to flow through the gaps between the fore-end part of the grinding stone portion and the working surface of the workpiece W. In such a case, a flow rate of the grinding liquid supplied through the through-hole 222 is rapidly decreased because of limitation on a supply pressure thereof, so that a cooling effect and cleaning action of the grinding liquid 220 cannot be exerted and thereby, powder of glass and loosed-off abrasive grains (workpiece powder and the like) 224 causes loading on working side surfaces 226a and 226b, inner and outer, of the workpiece W and the surfaces of the inner/outer sides of the grinding stone section 218 of the core drill 212 (FIG. 30). With such loading on the surfaces, a cutting ability of the core drill 212 is decreased and thereby, the core drill 212 quickly decreases its drilling speed.
In order to solve such a problem, there has been adopted the following process, in which drilling is continued till the outer end part of the grinding stone portion 218 progresses down to a depth a little larger than a height of the grinding stone portion 218; after the core drill 212 is temporarily stopped, the core drill 212 is extracted from the workpiece; powder of glass and loosed-off abrasive grains (workpiece powder and the like) 224 loaded on working side surfaces 226a and 226b, inner and outer, of the workpiece W and the surfaces of the inner/outer sides of the grinding stone portion 218 of the core drill 212 are removed; and then the drilling is restarted. For this reason, there has been arisen another problem, since a drilling time required is longer and thereby a cost is increased.
Furthermore, since the face of the outer end face of the grinding stone portion 218 of the conventional core drill 212 is of a flat surface, stresses arise in the workpiece such as glass across a broad area R confronting the outer end face of the grinding stone portion 218 through which the grinding stone portion 218 passes (hereinafter referred to as pass-through area) on completion of the hole forming (FIG. 31). As a result, there has arisen still another problem in a conventional drilling technique, since the defects such as cracks and indentation caused by chipping are easy to be generated in a broader pass-through area R than a drill diameter, which entails deterioration in quality.
While there have generally been employed an outer-diameter blade, an inner-diameter blade, a core drill which are provided with a tip portion or a grinding stone portion, in which diamond abrasive grains of the highest hardness available for cutting of and hole forming in hard material are used, when a material that has stickiness such as metal is cut, a diamond tip portion and a diamond grinding stone portion get higher in temperature and as a result, the diamond tip portion and the diamond grinding stone portion have chances to burn due to the high temperature. In such cases, there have especially preferably been employed a CBN outer-diameter blade, a CBN inner-diameter blade and a CBN core drill that are respectively provided with CBN tip portions and a CBN grinding stone portion, which are inferior to diamond in hardness but superior to diamond in heat resistance.
CBN is a boron nitride having a sphalerite crystal structure in a cubic system and alternatively called borazon. Since CBN not only is excellent in heat resistance, but also is the second to diamond in hardness, CBN is well used in various kinds of tools and as loose abrasive grains.